Closure operators have been designed to actuate closures such as a garage door in opening and closing movements. Such door operators have utilized a continuous chain having one driven sprocket and one idler sprocket near opposite ends of a guideway for a slidable member connectable to the door to effect these opening and closing movements. Such door operators have usually had a reversible motor and in all cases the chain is loaded in tension for both opening and closing movements.
Another type of door operator includes a rotatable worm or screw rotating in an elongated guideway which also guides a slidable member connectable to the door, the slidable member carrying a partial nut engaging the screw so that upon motor drive rotation of the screw, the door is moved in opening or closing movements depending upon the rotational direction of the screw. The relatively rigid screw is made of metal and is loaded in tension and compression forces for opening and closing movements, respectively.
In the chain drive type of door operator, the guide channel for many years has been cut into two or three pieces for compactness of the shipping container and then spliced together end-to-end at the garage site for use. In recent years, the screw drive type of door operator has had the guide rail cut into two or three pieces and then spliced together at the garage site use. This, however, requires the screw to be also cut into two or three pieces and the joints between these screw sections can weaken the entire screw and door operator.
Another construction of a door operator is suggested in U.S. Pat. No. 3,252,503, wherein an elongated, flexible belt or tape is motor-driven by a worm gear engaging worm teeth apertures in the tape and the tape is guided in a rigid, elongated track which also guides a slidable member connectable to the door for opening and closing movements. The tape has two discrete ends rather than being a continuous loop, is loaded in tension for opening movements of the door, and is designed to be loaded in compression for closing movements. This patent shows the door operator in suggested use with a sectional garage door rolling on a track which is generally vertical at the closed position and generally horizontal at the open position of the door.
A deficiency in this type of tape drive door operator when it is actually constructed and attempted to be operated is that the flexible tape has limited strength both for tension forces during opening and compression forces during closing. Also for the door operator to be commercially marketable throughout the United States, it must meet UL requirements and be satisfactory for use with the great majority of garage doors, including not only the sectional doors riding on a curved track but also slab or one-piece doors which are currently prevalent in the west. A first type of slab door of one piece moves upwardly and outwardly to a position partially in and partially outside the garage as a canopy in a generally horizontal position. A second type of single slab type door is one which moves on hardware upwardly and inwardly to a position entirely within the garage into a generally horizontal attitude. To be commercially merchandised in the United States, both the screw drive and chain drive types of door operator must operate satisfactorily with at least these three different types of garage doors, and with such types in a full range of common door sizes. In either of these two types of slab doors, the load on the door operator is considerably greater than in a multiple sectional door rolling on a track, because in such sectional door the initial starting opening movement of the door is similar to breaking the knee of a toggle, which is a relatively small force, easy opening movement.
The flexible tapes commercially available for this suggested use as a garage door operator are tapes with punched holes for a drive sprocket rather than a worm gear, and such tapes have been used successfully in light-load applications such as window lift mechanisms in automobiles. However, such tape which is suitable for such light-load applications has been found to be unsatisfactory in life tests for garage door operators because the web between adjacent apertures is stripped or sheared from the tape at the drive sprocket.